This invention relates to a process for the preparation of phenylphosphonous dichloride. More particularly, the present invention relates to a process for preparing phenylphosphonous dichloride in an electrically-heated fluid-bed reactor.
Phenylphosphonous dichloride is an important industrial intermediate which is used in the manufacture of the insecticide EPN, in the manufacture of nylon stabilizers and in the manufacture of organophosphorous compounds.
Of the several known methods by which phenylphosphonous dichloride can be prepared, the "hot tube" process and the "autoclave" process are perhaps the two most prominent.
In accordance with the basic hot tube process, benzene and phosphorous trichloride are vaporized to form a mixed vapor stream which is then caused to come into contact with the surface area of a "hot tube". The temperature of the surface of the hot tube is typically maintained at about 600.degree. C. through the use of internal electrical heaters.
An improved hot-tube process, wherein monochlorobenzene is added to the reaction mixture, is taught in U.S. Pat. No. 3,029,282.
The basic autoclave process for preparing phenylphosphonous dichloride is described in U.S. Pat. No. 3,874,394, which also teaches that improved yields can be obtained by maintaining a specified relationship between reaction time, reaction temperature and the ratios of phosphorous trichloride and elemental phosphorous to monochlorobenzene present.
Each of these two processes are characterized by certain disadvantages. For example, the hot tube process is subject to formation of tarry residues (about 20-30 grams residue can be formed for every 100 grams phenylphosphonous dichloride produced), which can lead to fouling of downstream equipment, and has a tendency to generate undesirable byproducts such as biphenyl, chlorobenzenes and chlorophenyl phosphorous dichloride.
The Autoclave Process, on the other hand, involves a high pressure reaction (Ca 1000 psig) which may be regarded as an undesirable feature in and of itself.
A process which would enable the preparation of phenylphosphonous dichloride without the need to encounter the fouling potential characteristic of the hot tube process and without the need to operate at high pressures, such as is characteristic of the autoclave process, would be highly desirable.
It has now been found that phenylphosphonous dichloride can be prepared in an electrically heated fluid-bed reactor, in the absence of high pressure and with the coproduction of substantially less residue than that produced by the hot tube process.